If a server response is not valid JSON, WooCommerce POS will throw a SyntaxError.
WooCommerce POS communicates with the WooCommerce REST API using JSON. If you are seeing a SyntaxError it means that the POS was expecting valid JSON but got something else instead, usually an error message from WordPress.
Unexpected token in JSON
Clicking on the 'i' info icon will display the raw output from the server. In the example below, we can see there is a PHP Notice from WordPress. The notice references the line of code which is causing the problem.
Example of SyntaxError modal - Unexpected token
In the above example you can see that the error occurs in the example-plugin/example.php file at line 15. If you are seeing a similar error to the example above, please do the following:
If possible, deactivate the plugin causing the error, this will allow you to continue using WooCommerce POS
Also contact the developer of the plugin causing the error, they are usually in the best place to provide a fix
Unexpected end of input
In some cases the server will return nothing at all, this results in an Unexpected end of input with no extra information.
Example of SyntaxError modal - Unexpected end
This occurs if the PHP error_reporting is disabled. In order to see the error message you should temporarily enable error reporting by setting WP_DEBUG to true in your wp-config.php file.
// Enable debugging
You should only enable debugging for the time it takes to copy the error message. Debugging should not be enabled on a live site as it can produce unexpected errors and could potentially be a security risk.